Skip to main content

Full text of "Text Book Of Mechanical Engineering"

See other formats


Appendix IV.

953

condition of stress at a t, Fig. 355, has not been propounded, we
are obliged to accept such forms as are the result of direct
experiment. In Fig. 893 are shewn six different forms of eye,
all of which have been used on bridges, and all of which have
been proved. In Mr. Shaler Smith's experiments the mode of
manufacture was tested as well as the proportions, and therefore
the results are probably the most reliable.

Pp. 443 an(l $5*

Example 68.A beam is supported at two points one-quarter of
its length from each end, and is loaded by three equal concentrated
weights placed at the ends and the centre respectively ; draw the
diagram of bending moment.

The arrangement of the loads is shewn in Fig. 894, and the
diagram of Bm is to be drawn on the subtractive principle. Firstly,
construct the trapezium A B C D, where EC or F D = W x \l. This

diagram shews the Bm which would be caused if Wj and W3 acted
only, and the beam would be thereby curved upward. But W2 will
produce a reverse curvature on the beam between e and f, while
mot affecting the parts a e and fb. This moment, whose maximum is

W   /

lv, x   W x f/, or half that at E C, must be subtracted at every
2    4

point between E and F, as shewn at C G D, and the remaining shaded
figure Is the true diagram of bending moment.

P. 471. Wind Pressure on Roofs.  Some years ago
Prof. Keraot, of Melbourne University, constructed a blowing
machine giving a fairly steady jet of air about one square foot in
sectional area, and to this he exposed numerous models of